The present invention relates to a camera signal processing apparatus and a camera signal processing method for processing a camera signal generated by a camera apparatus of single-plate type. More particularly, the present invention relates to a camera signal processing apparatus and a camera signal processing method for computing a correlation value indicative of a correlation between interpolated values of pixels when a luminance signal or a color difference signal is generated from an imaging signal generated by a solid-state image sensor.
In a camera apparatus of single-plate type using a solid-state image sensor such as a charge coupled device (CCD) image sensor (hereafter simply referred to as a CCD), a color filter for transmitting lights corresponding to R (Red), G (Green), and B (Blue) is arranged on the CCD. In this color filter, a region for transmitting a red light, a region for transmitting a green light, and a region for transmitting a blue light are formed in matrix. For example, these regions are arranged as G, R, G . . . or B, G, B . . . horizontally. The light that passed each region of the color filter is inputted in the CCD. Then, pixel data G, pixel data R, and pixel data B are generated from the pixels corresponding to the R, G, and B regions of the color filter.
In this camera apparatus, a luminance signal and a color signal are generated based on the lights inputted in the CCD.
The CCD used in the above-mentioned camera apparatus is arranged with a color filter having R, G, and B for each pixel. The R, G, and B regions are arranged as R, G, R, G, . . . horizontally for example. In this camera apparatus, a color signal is generated in correspondence with the color filter arranged for each pixel. Therefore, in this CCD, in a pixel for which the color filter for transmitting a red light is arranged, the pixel data G and the pixel data B corresponding to G and B respectively are not generated, making it necessary for the data corresponding to G and B to be generated by interpolation.
In the above-mentioned camera apparatus, a method of processing a luminance camera signal generated by the CCD for example is known in which, for reading all pixels, pixel data is generated by performing arithmetic mean on the pixel data corresponding to four pixels, namely two vertical pixels and two horizontal pixels of the CCD.
In the single-plate camera apparatus, when generating pixel data by interpolation, correlation values indicative of correlations in vertical and horizontal directions are detected. In this detection, the signals of pixels arranged around are calculated by use of a filter to obtain the correlation value in vertical direction and the correlation value in horizontal direction. Further, in this camera apparatus, the pixel data obtained by interpolation is weighted by use of the obtained correlation values.
However, in the above-mentioned camera apparatus, the detection of a correlation value by the above-mentioned technique may fail to correctly detect the relationship between vertical correlation and horizontal correlation in the pixel data generated by the CCD.
Namely, the relationship between vertical correlation and horizontal correlation may not be correctly computed due to the aspect ratio of the CCD or a distortion or noise caused when an analog signal outputted from the CCD is detected or a high-frequency signal difficult to be detected for example.
If the relationship between vertical correlation and horizontal correlation is not correctly computed, it is difficult to determine in which of the vertical and horizontal directions the correlation is higher.
It is therefore an object of the present invention to provide a camera signal processing apparatus and a camera signal processing method capable of varying the relationship between vertical correlation and horizontal correlation by considering a signal distortion caused by the CCD for example.
In carrying out the invention and according to one aspect thereof, there is provided a camera signal processing apparatus comprising: a correlation detector for detecting a horizontal correlation value and a vertical correlation value for indicating degrees of correlation in horizontal and vertical directions of interpolated pixel data generated based on a position of pixel data detected by a solid-state image sensor and pixel data around that position and detecting a horizontal correlation value and a vertical correlation value for weighting the interpolated pixel data; a normalizing circuit for normalizing the horizontal correlation value and the vertical correlation value detected by the correlation detector to generate a normalized value indicative of a relative value between these correlation values; and a correcting circuit for adding a predetermined correction value to the normalized value generated by the normalizing circuit.
In carrying out the invention and according to another aspect thereof, there is provided a camera signal processing method comprising the steps of: detecting a horizontal correlation value and a vertical correlation value for indicating degrees of correlation in horizontal and vertical directions of interpolated pixel data generated based on a position of pixel data detected by a solid-state image sensor and pixel data around that position and detecting a horizontal correlation value and a vertical correlation value for weighting the interpolated pixel data; normalizing the horizontal correlation value and the vertical correlation value detected in the correlation detecting step to generate a normalized value indicative of a relative value between these correlation values; and adding a predetermined correction value to the normalized value generated in the normalizing step.